Tony Blair's long-awaited announcement on troop withdrawals from Iraq may inject a note of optimism into the biggest "legacy issue" hanging over his looming retirement.

Mr Blair will want some good news from Iraq

But, even as it was being welcomed by many, there were claims it was either too little too late or, alternatively, too much too soon.

The prime minister has certainly been eager to see some good news out of Iraq in the run up to his departure, so he will have to dismiss suspicions it was being motivated by domestic political considerations.

As he stressed in the Commons, it was always planned that the announcement would come in the wake of the completion of Operation Sinbad, which was designed to hand over frontline security in Basra to Iraqi forces.

Turn the tide

The beginning of the draw-down is believed to be some time in May, although Mr Blair refused to be too specific, coinciding with the expected announcement from the prime minister of a timetable for his departure from Downing Street.

The details set out by the prime minister in the Commons - of a cut from 7,100 to 5,000 by the end of summer with further cuts by the end of the year if all goes well - will be studied closely.

Local forces are taking control in Basra

It has been suggested, for example, that the withdrawal process has actually been slowed after pressure from President Bush as he mounts his own policy of sending a "surge" of troops into Baghdad in an attempt to turn the tide in that part of the country.

It is always pointed out that conditions in Basra and Baghdad are entirely different and that, as senior military chiefs have previously suggested, the removal of British troops in the south may improve the situation further by removing a possible provocation.

Mr Blair appeared to agree with that point in a BBC interview on Sunday when he said he did not want British troops "to get in the way" of progress in Basra.

Intensify attacks

The question being asked is whether this is the beginning of the end of UK military involvement in Iraq - something that is already being used by President Bush's opponents to demand a similar move from him.

If it is the beginning of the end, is it a withdrawal in the wake of success or is it, in effect, retreat in the face of an impossible situation?

Military experts have pointed out the dangers of any withdrawal as insurgents intensify attacks in an attempt to suggest they have got British troops on the run.

There are still questions as well, raised most recently by Lib Dem leader Sir Menzies Campbell, that the US troops surge in the north lead to a displacement of violence into the south.

The plan is for a considerable number of British troops to withdraw to a base outside Basra where they will be available to support the Iraqi forces as necessary.

But any decision to send them back into the city in response to an increase in violence could prove disastrous for the prime minister.

Many, like former Liberal Democrat leader Paddy Ashdown, believe this points to only one conclusion. That, for good or ill, this is the beginning of the end of UK forces' involvement in Iraq.